Research Topics

Research is the cornerstone of the program. Thus, each student admitted to the program is expected to take part in a research project. A major contribution to the student's education in this program comes from the experience gained carrying out research and design on the fundamentals of new technologies and their application to buildings. The research project will normally be on a subject under current investigation by an interdepartmental team of faculty and students or by an individual faculty member. This research is typically used by a student to fulfill the thesis requirement for the degree. The sponsored research gives the students exposure to both practitioners and other international scholars working with important issues in their field of interest. Many students serve as research assistants, receiving financial support to cover tuition and some living expenses.

Building Ventilation and Diagnostics

CoolVent , developed in the Building Technology Research Group over the last decade, is a simulation tool for early design of buildings that predicts the effects of natural ventilation on the building's internal temperatures and airflow rates. The tool, the first of its kind, allows simulating time-varying thermal conditions for a typical day of a month (based on weather data), accounting for the effects of thermal mass, and night cooling. CoolVent calculations are based on a multi-zone model with coupled energy and flow equations, and rely on two basic assumptions: uniform temperature distribution in each zone (floor) of the building, and unidirectional air flow through its openings. It has been successfully validated for conditions that match these two assumptions. However, in situations where the thermal stratification of air in a room is too strong, the predictions of CoolVent need to be improved.

My doctoral work focuses on understanding air thermal stratification in a naturally-ventilated room. My goal is being able to predict the strength of air stratification in a room, and the effect that this density gradient has on the temperature of the room's occupied zone and the air flow in and out of each zone.

Ventilation Shaft Modeling

In the United States and most developed countries buildings consume roughly 40% of the nation’s primary energy, a number that is steadily growing. For all US buildings, space cooling and ventilation consume 16% of building energy use. However, in cooling-dominated climates, this percentage is significantly higher. One strategy for decreasing this energy consumption is to use natural ventilation (NV), a passive cooling and ventilating technique that utilizes natural forces like wind or buoyancy differences to bring outside air into the building.

A fundamental limitation of NV is the required climate. No building owner will naturally ventilate his building if outside air temperature or humidity levels are unacceptable for indoor comfort conditions. Thus, a rare few climates allow for a purely naturally ventilated building. This limitation in NV has lead to hybrid ventilation (HV) – a mix of NV and more traditional mechanical heating, ventilation, and air conditioning (HVAC) methods. While HV systems predictably require a larger capital investment than either a NV or mechanical HVAC system, the cost savings of an HV system over its lifetime could conceivably more than pay back the initial investment.

A major gap currently exists in our ability to predict the performance of an HV system – thus its energy and cost savings – when buoyancy-driven flow is present. Airflow network tools exist that predict airflow driven both by wind and buoyancy effects, however the assumptions used to model buoyancy-driven flow are often unrealistic. Such assumptions include a uniform temperature distribution in the ventilation duct, when actually the distribution is highly stratified especially near the duct entrance, or unidirectional flow in the duct, when bidirectional flow is likely due to the presence of large eddies in the flow.

The aim of this research is to deepen the understanding of NV to allow for better modeling in airflow network tools used in building energy modeling software to more confidently predict the energy and cost savings of a hybrid ventilation system.

System Identification and Optimal Control for Mixed-Mode Cooling

The majority of commercial buildings today are designed to be mechanically cooled. To make the task of air conditioning buildings simpler, and in some cases more energy efficient, windows are sealed shut, eliminating occupants’ direct access to fresh air. Implementation of an alternative cooling strategy–mixed-mode cooling–is demonstrated in this thesis to yield substantial savings in cooling energy consumption in many U.S. locations.

A mixed-mode cooling strategy is one that relies on several different means of delivering cooling to the occupied space. These different means, or modes, of cooling could include: different forms of natural ventilation through operable windows, ventilation assisted by low-power fans, and mechanical air conditioning.

Three significant contributions are presented in this thesis. A flexible system identification framework was developed that is well-suited to accommodate the unique features of mixed-mode buildings. Further, the effectiveness of this framework was demonstrated on an actual multi-zone, mixed-mode building, with model prediction accuracy shown to exceed that published for other naturally ventilated or mixed-mode buildings, none of which exhibited the complexity of this building. Finally, an efficient algorithm was constructed to optimize control strategies over extended planning horizons using a model-based approach. The algorithm minimizes energy consumption subject to the constraint that indoor temperatures satisfy comfort requirements.

The system identification framework was applied to another mixed-mode building, where it was found that the aspects integral to the modeling framework led to prediction improvements relative to a simple model. Lack of data regarding building apertures precluded the use of the model for control purposes.

An additional contribution was the development of a procedure for extracting building time constants from experimental data in such a way that they are constrained to be physically meaningful.

Ventilation Control Strategies

Building space-conditioning systems often perform at poor part-load efficiencies because there is limited information feedback from individual offices and because part-load operation has led to large throttling losses. The increased use of microelectronics and power electronics in building control systems offers two benefits for ventilation systems: first, fans can be controlled not by adjusting dampers that throttle flow but by regulating the speed of the motor; and second, by communicating with digital rather than analog flow-regulation dampers in each occupied space, the central fan can be slowed to the speed that minimizes pressure drops across these dampers. A recently completed program tested and analyzed both of these benefits, with the goal of quantifying energy savings and providing to building owners, control manufacturers and electric utilities the information needed to make informed decisions about investing in new technologies. The performance of ventilation systems was monitored in several buildings and models were developed to correlate fan power with airflow and pressure.

Electric Metering and Diagnostics

Common electric meters are well developed electromechanical devices with little or no intelligence. The electric utility industry requires extensive load survey data to plan for future power generation needs and to prove the efficacy of utility-supported conservation programs. Customers would benefit from the same data, to assess energy usage and to detect and diagnose equipment faults. The Building Technology Program has joined the Laboratory for Electromagnetic and Electronic Systems at MIT to design and develop a meter that can separate loads from measurements made at a single point within a commercial building, to reduce or eliminate the need for expensive submetering of individual pieces of equipment.

Simulation of HVAC System Performance

Heating, ventilating, and air- conditioning (HVAC) systems are often poorly controlled. Engineers have not been able to rapidly prototype HVAC systems, in simulation, and assess the performance of existing or innovative control systems, including interactions between individual feedback control loops. MIT and Loughborough University, UK, have joined forces to develop a simulation test-bed for the development and analysis of control systems for a large class of HVAC systems.

Building Energy Studies

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Assessing Energy-Saving Potential of Different Roof Systems

Student: Stephen Ray, PhD student in Mechanical Engineering

Previous studies suggest potential for energy savings through cool and green roofs, but do not always consider the many factors that affect potential savings or the relative advantages of different technologies. To further investigate these factors, a tool has been developed to allow architects the ability to quickly assess the energy-saving potential of different roof systems. A first principles heat transfer model has been developed for each of the roof technologies, with particular care for green roof heat and mass transfer. Experimental data from Japan and Florida validate the models by predicting roof surface temperature. This model is incorporated into the existing MIT Design Advisor to allow users the ability to include roofing systems in their energy analysis of a building.

Infrared Thermography for the Comparison of Building Energy Envelope Performance in Residential Homes

Student: Kaitlin Ryan Goldstein

There are 120 million residential homes in the United States that are responsible for 20% of the United States' total carbon emission. As energy has been relatively cheap for the past 20 years, the efficiency of these homes has been an afterthought during the construction process. We are thus left with an existing building stock with the potential to improve their consumption through efficiency measures alone from 15-40%.

In order to make a difference in these homes we must first understand where the problems are, and, which homes are the greatest consumers. Unfortunately, the current means by which this is accomplished, home energy audits, are time-consuming, involve full participation and commitment form the home-owner, and require a large, as of yet, untrained labor force. While these audits are essential there needs to be an independent means by which to understand the homes' energy consumption, and in particular, heat transfer ( the loss or gain of energy) through the building envelope. This includes all of the parts of the building that interact with the outdoors including its exterior walls, windows doors and roof.

To understand energy consumption in buildings and to compare one home to another in a fast, efficient manner, we are developing a suite of tools centered around infrared thermography. Our research looks to take these pictures which give a representation of surface temperatures on the building surface from a remote vehicle driving past the neighborhood homes. The next step, and the focus of this research is to utilize these maps of surface temperatures along with measurements of prevailing external conditions to understand how the homes are interacting with their surroundings. From this, we will be able to back out the insulation, or R-values of the homes. We also hope to characterize how heat moves through the windows and doors and how much air is escaping from inside the building through infiltration.

The end goals is to be able to compare one home to another in a neighborhood and provide recommendations as to which homes should be targeted for retrofit and the most effective means by which to improve their envelopes. In addition, we hope to develop a map of efficiency potential within a neighborhood and calculate the respective returns on investment for various suites of improvements. This method is not only fast and efficient in the identification process but it also allows for return examination through the same mechanism and the comparison of performance pre and post retrofit to determine the efficacy of improvements.

Efficient Cooling Technologies for the Built Environment

One promising method for reducing the energy consumption of cooling systems is to reduce the pressure rise across the refrigerant compressor, a systems approach known as low-lift cooling that was pioneered by Armstrong at the Masdar Institute of Science and Technology. This requires increasing evaporator temperatures and decreasing condenser temperatures. Radiant cooling systems promote the former, through use of water at higher temperatures than the output of all-air cooling systems. Thermal storage in building mass promotes night cooling, when outdoor conditions allow lower condensing temperatures. Efficient motors and variable-speed motor drives for the compressor and auxiliary fans and pumps provide efficient low-load operation. Finally, a dedicated outdoor air system meets latent cooling loads.

Operation of this system to maximize performance requires model-based predictive control, which in turn demands component models that accurately capture component operation under a very wide range of conditions. Research at MIT includes test-stand measurements of component performance, physics-based modeling with parameter identification from measurements, identification of optimal operating points for a given cooling load and indoor and outdoor conditions, and evaluation of the performance of conventional and low-lift systems in a full-scale test chamber.

MIT Design Advisor

The MIT Design Advisor[3] is a multi-purpose simulation tool designed to evaluate the performance of advanced building facade systems. By defining a set of building parameters and operating conditions, a building designer can simulate in realtime the energy requirements (heating, cooling, and lighting) and comfort levels (daylight, temperature) of a proposed design. This simulation presents the user with a convenient method of examining facade performance.

Existing analysis tools are typically very complicated, difficult to learn, and require a fully developed building design, making them unsuitable for preliminary design analysis. Efforts to improve building efficiency are typically left for the later stage of the design process, after the critical design decisions have already been made. Because early stage design decisions can have a dramatic impact on building performance, we offer this tool as a fast, simple way for a non-technical user to evaluate preliminary designs.

Building codes help to ensure that buildings meet a minimum standard of energy efficiency. To assist building designers, we are implementing a tool to test a proposed building design against two building code standards: ASHRAE Standard 90.1-2001, and the UK Building Code Part L.

The Design Advisor allows a user to simulate a single side of a building facade or an entire four-sided building. The four-sided simulation assumes that the features on each side of the building are identical. In practice, this is often not the case, and so we are developing added functionality to simulate a building with four different sides.

Building Materials and Construction

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New Insulation for Retrofitting Existing Buildings

Student: Ellann Cohen

Buildings consume too much energy. For example, nearly 14% of all the energy used in the United States goes towards just the heating and cooling of buildings. Many governments, organizations, and companies are setting very ambitious goals to reduce their energy use over the next few years. Because the time periods for these goals are much less than the average lifetime of a building, existing buildings will need to be retrofitted.

There are two different types of retrofitting: shallow and deep. Shallow retrofits involve the quickest and least expensive improvements often including reducing infiltration around windows, under doors, etc and blowing more insulation into the attic. Deep retrofits are those that involve costly renovation and typically include adding insulation to the walls and replacing windows. A new, easily installable, inexpensive, and thin insulation would move insulating the walls from the deep retrofit category to the shallow retrofit category and thus would revolutionize the process of retrofitting homes to make them more energy efficient.

For my thesis, I am working on the development of a new, easily installable, inexpensive and thin insulation. The basic design idea for this new insulation is to have a silica aerogel (the lowest thermal conductivity material known today) based insulation that will have superior insulative properties as compared to conventional insulations. It will also be thin enough that it can be installed on the inside walls of buildings while still adding substantial R-value.

Traditionally the envelopes of houses are site-assembled from basic components with separate materials serving as the structural members, the weather shield, and the thermal insulation. In this recently completed project composite materials were developed that combined these separate functions. In addition, a construction system well suited to automated fabrication and simple field assembly is being developed. A proof-of-concept roof system, the first product of this research, is based on innovative design and analysis strategies and is compatible with conventional systems while minimizing house-specific design. The roof components include thin-ribbed stress-skin panels, a multi-function ridgebeam and a spline-connection scheme.

Advanced Thermal Insulations

New buildings and renovated existing buildings, as well as appliances, can be made more energy efficient by the use of insulations which are more compact for the same level of performance. Recently completed research on closed-cell foam insulation improved its insulating performance and at the same time allowed it to be manufactured with elements which are not hazardous to the environment (in particular which do not deplete the ozone layer). Advanced insulation, which includes a composite of foam and vacuum technology, was also developed.

Thermal Insulation for Developing Countries

In a number of resource-poor developing countries, buildings are constructed of masonry material without thermal insulation. In winter, these buildings are uncomfortably cold or even uninhabitable. MIT is developing a low- cost thermal insulation for such countries. The feedstock for the prototype insulation is straw, a by-product of wheat threshing. The investigations have focused on straw density, the type and amount of binder needed to make straw panels, thermal and structural tests, and means of attaching the panels to stone walls and applying a surface finish. MIT students have made on-site surveys and prototype tests in Pakistan.

Identification and Promotion of Locally Sustainable Building Construction Methods for Latter-stage Slum Improvement

Slum-improvement strategies are a result of conclusions drawn from the most successful projects that have addressed city-center squatter communities. While the factors that need to preside in successfully addressing the needs of the residents of these settlements are complex and necessarily mutable depending on location and overall purpose of the project, it has been recognized by a wide range of organizations that the upgrading, as opposed to physical removal, of slums is a better long-term solution. The creation of mechanisms, financial, political and institutional, that provide a well-conceived package of service infrastructure and the establishment of land tenure are the most important first steps in alleviating the health risks and economic hardships that the residents endure. Later, the sustainability of these improvements should lead to an increased desire to upgrade the physical quality of the dwelling units themselves. This project proposes the identification of locally sustainable methods of construction for dwelling upgrade as a strategy for catalyzing the development of viable income producing activities within and adjacent to the confines of the slum itself. This promotion is in the service of establishing a sustainable process of continual slum-improvement after the work of this project has been completed. The identification of construction methods and the consideration of innovative materials and assembly systems will contribute to a realistic proposal for a set of building components to be used in the upgrade of dwelling units. The location of the project is to be determined.

Center for Sustainable Materials and Building Envelopes

The study of sustainable materials necessarily involves an extremely large set of scientific and economic criteria to reasonably establish a productive comparative analysis. While a number of systems have been proposed and developed, none has secured a clearly predominant position over all others. Therefore, it is necessary to glean from a great number of sources the necessary information and rating criteria to offer a current and productive assessment of the state of rating materials for their sustainable value. This proposal offers to study the available literature and tools for determining the sustainability of construction materials for the purpose of:

establishing the state of the art of ratings systems and their attendant criteria,

identifying the most recent and important innovations in sustainable material technologies, and identifying key areas for further research.

Three-dimensional Fiber Textile Composites for Use in Construction

Three dimensional fiber composites have resulted from a search for viable alternatives to 2D composite laminates. As a result of increasing concern regarding the difficulty with which 2D composites have been able to address delamination from impact, in-plane shear stresses and transfer of axial and bending stresses between adjacent composite elements, 3D fiber textile composites (FTCs) have recently received greater attention. For many reasons, the industrial application of 3D FTCs has lagged far behind the use of 2D composites in high-performance industries such as aerospace and large-scale marine structures. However, several isolated yet noteworthy applications have been implemented in less demanding performance scenarios for civil and architectural structures. The lower level of performance requirements makes the use of 3D FTCs a possible way in which to lighten and strengthen typical structural and non-structural components used in civil and architectural structures. In addition it is possible that 3D FTCs may provide a versatile medium for the inclusion of specialized fibers for a variety of enhanced properties. One particularly interesting possibility arises from the inclusion of smart or responsive fibers within the architecture of the 3D FTC.

Natural Fiber Reinforcement of Large-Scale Composite Polymer Panels

Recently, natural fibers (NF) have been investigated as filler materials capable of serving as localized tensile reinforcement and volume fillers within several types of polymer matrices. A number of natural fibers have been under continued investigation for use in natural fiber reinforced polymer composites (NFRC); including wood fiber, jute, sisal, kenaf, flax, wheat straw and bamboo. These fibers have been coupled in a matrix primarily composed of two commodity plastic matrix materials: polyethylene (PE) and polystyrene (PS). While specific mechanical properties of natural fibers vary according to the particular fiber, the overall performance of natural fibers lies within a relatively tight range as a result of similar molecular composition. An increasing amount of interest has developed over the past few years for NFRCs because of their ease of production, subsequent increase in productivity, cost reduction, lower density and weight and use of renewable resources. The automobile industry has begun to apply NFRCs in a variety of exterior and interior panel applications. The significant weight savings and the ease and low cost of the raw constituent materials have made NFRCs an attractive alternative material to glass and carbon fiber reinforced polymer composites. However, further research needs to address significant material and production obstacles before commercially available NFRCs are widely used in architectural and civil works.

Fiber Reinforcement of a Composite Exterior Wall Panel for the Purpose of Resisting High-velocity Impact Events

The introduction of fiber reinforcing into the exterior finish component of an exterior wall assembly may aid in preventing catastrophic failure of the integrity of the wall during events in which high-velocity impact is likely. The most important events to address are those conditions caused by naturally occurring high winds and blast events. During these events, it has been observed that a wide range of objects become lethal projectiles that pose significant hazards to both personal injury and property damage. While layered polymer composites have demonstrated an increasing level of resistance to projectile impact, significant difficulties remain that require further research. In particular, delamination from low and high velocity impact has been a major problem that threatens the structural integrity of the panel. The use of composites for exterior sheathing is a growing area for research and architectural and civil applications in the US, and especially in Europe and Japan. For the advancement of the use of large-scale composite panels for exterior sheathing, further research regarding resistance to impact should be undertaken.

Self healing fibers have received a significant level of interest primarily with applications for inclusion in reinforced concrete as a crack management strategy. These smart fibers have been added as discrete elements within the concrete matrix. The self-healing fibers are primarily fluid-filled hollow capillaries that contain a bonding agent that, when released, slow or prevent the spread of a crack through the concrete matrix. Self-healing fibers have also been proposed as a strategy for addressing debonding events between the concrete matrix and reinforcing bars. Another application is proposed for this type of smart fiber. The management of the transfer of heat through an exterior wall is an important aspect of the thermal performance of that envelope; one that is substantially compromised by air infiltration and exfiltration. Standard building practice, especially in residential construction, usually requires that a membrane be applied to the building volume to reduce the movement of air between the interior and exterior. Any discontinuities in this membrane may allow for the passage of air to and from the exterior. Self-healing fibers, as an inclusion within the weave of an air/vapor barrier textile, will be studied as a strategy for passively sealing the miscellaneous discontinuities that arise during the application and lifetime of the membrane.

Incorporation of a Smart Fiber Network within a 3D Fiber Textile Composite Near-net Preform Structural Member for Remote Structural Monitoring

3D fiber textile composites are a type of fiber architecture that allows for the inclusion of a variety of fiber types within a three-dimensional near-net preform network. The inclusion of monitoring smart fibers within the architecture of the woven material allows for the through-member permeation of a fibrous sensor material. Typical fiber materials used for stress and strain monitoring are optical glass fibers linked to a central processor. In this way it is possible to gather important information regarding the health of a structure during construction and during its lifetime from a remote location. The study proposes to evaluate fibers for inclusion within a 3D FTC structural member as well as propose various sensor network architectures most productive for the applications listed. The materials chosen need to conform to the stresses inherent in the pultrusion and weaving processes during the production of the standardized structural forms.

Daylighting

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Research in daylighting focuses on increasing how much natural light we can use in buildings, so as to decrease energy consumption for lighting, heating and cooling, improve comfort and well-being, generate aesthetical value, and provide a connection to the outside.

Current projects, involving students with a variety of backgrounds, range from developing experimental and simulation-based design tools for architects and architecture students so as to more efficiently integrate daylight in a building design process, to the construction of a new kind of instrument for optimizing advanced glazing and shading systems. Another major focus is concentrating on the development of new daylighting metrics, including health aspects, or of new facade or window systems.

Structures

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Understanding A Building Material: Material Flow Analysis of Concrete in the United States

Principal Investigator: Manshi Low

Currently, little is known about the management of massive building materials flows. This has serious implications in how the growing volume of construction and demolition (C&D) building waste would be dealt with. A Material Flow Analysis (MFA) of concrete is proposed to increase the transparency of the movements of a widely-used building material. The MFA would provide the mass quantities of raw materials and concrete from the extraction phase (cradle) to the post-use phase (cradle) moving through the U.S. economy for a given year. Ideally, the volume of the concrete as building stock and its average residence time in the anthroposphere could be quantified.

International Studies

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Interaction of Buildings and the Urban Environment

Building energy use is often modeled with no regard for the urban location of most buildings. Weather data typically come from airport meteorological stations where temperatures and wind speeds differ from those in urban canyons. To improve estimates of building energy use, the U.S. DOE EnergyPlus building energy model is being coupled to an urban surface energy balance from the French National Center for Meteorological Research. This coupled approach captures the influence of heat flows from buildings on street-canyon temperatures and the reciprocal influence of these temperatures on the heat flows and energy use of space conditioning equipment. Results show the significant contribution to the urban heat island effect from space cooling waste heat. A complementary study focuses on predicting street-level airflows and turbulent exchange between street canyons and the portion of the surface layer above the canyons. The work will be applied to investigations of the impact of increased urban development on the urban environment. Much of the effort in focused in Singapore, as part of the Singapore-MIT Alliance for Research and Technology (SMART)